1. Field of the Invention
The present invention relates to a method and system of reducing handover time in a mobile Internet Protocol (IP) network, and more particularly, to a method and system by which, when a Mobile Node (MN) carries out a handover between two sub-networks managed by a single Foreign Agent (FA) having two or more sub-networks, a Home Agent (HA) registration for the Mobile Node (MN) may be omitted in order to minimize a handover delay.
2. Description of the Related Art
Mobile Internet Protocol (IP) is an Internet Engineering Task Force standard communications protocol designed to allow users of mobile devices moving between different networks while having a permanent IP address. Mobile Internet Protocol has two kinds of entities, i.e., a Home Agent (HA) storing information of mobile nodes whose permanent addresses are stored in the home agent's network, and a Foreign Agent (FA) storing information of mobile nodes visiting the foreign agent's network.
In a contemporary mobile Internet Protocol (IP) network, in a handover of a Mobile Node (MN), when the Mobile Node (MN) is migrated from one sub-network to another, this Mobile Node (MN) recognizes its own presence in a new sub-network based on either prefix information or lifetime information of an agent advertisement message, received from the new network, or based on the termination of lifetime of an agent advertisement message when the agent advertisement message is not received until the lifetime is terminated.
Then, the Mobile Node (MN) sends a Home Agent (HA) registration request message to the Home Agent (HA) via a Foreign Agent (FA) in order to inform the Home Agent (HA) that the Mobile Node (MN) is migrated to a new network. When the registration request message is received, the Foreign Agent (FA) generates a pending registration request entry of a visitor list using message information, and then transmits the registration request message to the Home Agent (HA).
Accordingly, the Home Agent (HA) updates mobility binding list information of the Mobile Node (MN) by using the registration request message, validates the registration request message, and sends the result on a registration reply message via the Foreign Agent (FA) to the Mobile Node (MN).
When the registration reply message is received, the Foreign Agent (FA) identifies the contents of the message. If the result of the registration request is successful, the Foreign Agent (FA) searches the visitor list for the pending registration request having the same Mobile Node (MN) home address, and registers as a normal entry. If the search result is unsatisfactory, the Foreign Agent (FA) discards the registration reply message.
Then, the Foreign Agent (FA) transmits the registration reply message to the Mobile Node (MN), and the Mobile Node (MN) judges whether or not the entire registration procedure is successful based on the result of the received registration reply message.
In the contemporary mobile IP network, however, when the Mobile Node (MN) carries out a handover, the registration request message is transmitted to the Home Agent (HA) via the Foreign Agent (FA) in all cases irrespective whether or not the handover is carried out between sub-networks of same Foreign Agent (FA), so that the mobility binding list managed by the Home Agent (HA) is updated. Therefore, in the case where handover happens in one Foreign Agent (FA), mobility binding list managed by Home Agent (HA) is not required to be updated. Therefore, in a contemporary handover process, a time delay due to unnecessary update of mobility binding list in the case where handover happens in one Home Agent (HA) should be eliminated to improve the efficiency of IP mobile system.